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J. Bacteriol., 04 1995, 2143-2150, Vol 177, No. 8
Copyright © 1995, American Society for Microbiology

Genes encoded on a cyanobacterial plasmid are transcriptionally regulated by sulfur availability and CysR

ML Nicholson and DE Laudenbach
Department of Plant Sciences, University of Western Ontario, London, Canada.

A cyanobacterial sulfur-regulated gene (cysR), which encodes a protein with similarity to the Crp family of prokaryotic regulatory proteins, has recently been isolated and characterized. Polyacrylamide gel electrophoresis of periplasmic protein extracts reveals that a cysR mutant fails to synthesize a 36-kDa polypeptide that is normally induced in wild-type cells that have been grown under sulfur-deficient conditions. The amino-terminal sequence of this protein was obtained, and a synthetic oligonucleotide was used to isolated a clone containing a 1.9-kb NruI-KpnI fragment from a Synechococcus sp. strain PCC 7942 genomic library. RNA blot analysis indicates that this fragment encodes a transcript that is detectable in wild-type but not cysR mutant cells that have been starved for sulfur. DNA blot analysis revealed that the 1.9-kb NruI-KpnI fragment is contained within the Ba4 BamHI fragment of the endogenous 50-kb plasmid pANL. RNA blot studies indicate that the accumulation of a large number of pANL transcripts is regulated by sulfur levels and CysR. DNA sequence analysis confirmed that the gene encoding the sulfur-regulated 36-kDa periplasmic protein is encoded on the Ba4 fragment of pANL. The sequence of the 36-kDa protein displays sequence similarity to the enzyme catalase, and two downstream proteins exhibit 25 and 62% identity to a subunit of a P-type ATPase complex involved in Mg2+ transport and a chromate resistance determinant, respectively. Surprisingly, a strain in which the putative chromate resistance gene was interrupted by a drug resistance marker exhibited increased resistance to chromate when grown in media containing low sulfate concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)


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